Left arm pain

I am 36 yr. old female with type II diabetes, which i control with meds and insulin.  I have been having slight chest discomfort and heartburn.  The chest discomfort is gone, but now i have pain from my shoulder down to my hand in my left arm.  I did an ekg about 2 months ago and my doctor put me on 12.5 mg of atenolol even though my blood pressure is 110/80.  She said my ekg reading came back with my heart rate jumping from 60 to 168 with no physical activity.  I am a programmer who sits behind a computer screen all day.  I haven't taken the atenolol for over a month due to it making me feel fatigued.  Most of my discomfort is in my upper part of my left arm.  I was wondering if I should be worried about it or does it sound more stress related due to aniexty.  The pain in not unbearable, just annoying.